Operation of turbo-machines, such as centrifugal impeller turbo-machines, generates significant amounts of acoustic noise. A dominant portion of acoustic noise generated by a centrifugal turbo-machine is due to an impeller blade rotating at a high rpm, which causes a high pressure side and a low pressure side to develop on the leading edge of the blade. This pressure differential generates pressure perturbations which propagate back upstream through the gas passage at the blade passing frequency, radiating out the fluid passage inlet of the turbo-machine as acoustic noise.
Multiple attempts have been made in the art to reduce this noise via the inclusion of inlet silencers. Inlet silencers are primarily effective in a lower frequency range than the frequency range of noise generated by the impeller blades. Other attempts at reducing the noise have resulted in unacceptable reduction in the performance of the turbo-machine.